1. Field of the Invention
The present invention relates to an inkjet recording head which incorporates a tank for containing ink, and an inkjet recording device including ink supplying means for supplying ink to the inkjet recording head through a needle.
2. Description of the Related Art
Image recording devices are used in diverse applications, for example, printers, copying machines, or facsimile machines, or recording devices used as output devices of composite electronic devices (including, for example, computers or word processors), or as output devices of workstations. These recording devices are constructed so as to record an image (including characters, drawings, designs, etc.) on a recording material (recording medium) such as paper or a thin plastic plate, with the image being recorded based on image information. One form of such a recording device for forming an image on a recording medium is an inkjet recording device which discharges very small ink droplets from a very small ink-discharge nozzle or opening. In general, an inkjet recording head of the inkjet recording device comprises a recording head body which includes an ink-discharge nozzle or nozzles for discharging ink droplets and a tank for containing ink supplied to the recording head body. The ink is guided from the tank to the recording head body. An energy generating member, such as a heat-generating element or a piezoelectric element, disposed close to the ink-discharge nozzle is driven based on a recording signal, causing ink droplets to be discharged from the ink-discharge nozzle and to stick onto the recording medium, whereby a recording operation is carried out. The inkjet recording device is what is called a nonimpact recording device, and has the advantages of, for example, being capable of performing a recording operation with high speed and on various types of recording media and producing almost no noise during the recording operation. Accordingly the inkjet recording device is widely used.
Among the different types of inkjet recording devices, a bubblejet-type inkjet recording head which discharges ink using heat energy can perform a recording operation with high resolution because its ink-discharge nozzles for discharging ink can be disposed very close to each other. In particular, a bubblejet-type inkjet recording head which uses an electrothermal converting member as an energy-generating source can easily be made more compact. In addition, the advantages of integrated circuit (IC) technology and micro-fabrication technology, which have improved considerably and which have become very reliable in the semiconductor field in recent years, can satisfactorily be made use of, so that high-density mounting can be easily achieved, thereby causing the bubblejet-type inkjet recording head to be advantageous from the viewpoint of low manufacturing costs.
Many methods of supplying ink to the tank of the inkjet recording head, such as an on-carriage tank method, a pit-in method, and a continuous supplying method using a tube, have been proposed. Among these methods, the continuous supplying method using a tube is primarily used in large recording devices and business recording devices because the capacity of the tank incorporated in the inkjet recording head can easily be made large, running cost is low, and the tank does not need to be frequently replaced.
As mentioned above, the inkjet recording head of such an inkjet recording device comprises a recording head body (discharge unit) and a tank for storing ink. Ink in a main tank that is fixedly provided at the recording device body is supplied to the tank (which is hermetically sealed) of the inkjet recording head through a tube. From this tank, the ink is supplied to the recording head body disposed downstream from the tank.
When the inkjet recording device is constructed in this way, since the tube and the tank are hermetically sealed except from the main tank, if, for example, no air bubbles are produced due to ink discharge or expansion or coagulation of dissolved air inside the tank of the inkjet recording head, an amount of ink which is the same as the amount of ink discharged is automatically supplied from the main tank to the tank of the inkjet recording head.
However, even a very small amount of air mixed in the ink gradually accumulates over time, and very small amounts of air can pass through, for example, the wall of the tube and gradually accumulate in the entire ink path. Therefore, the amount of air in the tank of the inkjet recording head increases over time, causing the amount of ink in the tank to gradually decrease. When the amount of ink in the tank decreases in this way, it is necessary to forcefully supply ink by, for example, suction generating means.
Here, the most generally used means for forcefully supplying ink supplies ink by providing a pressure difference between the main tank and the tank of the inkjet recording head by generating negative pressure in the tank by a suction generating device such as a pump. In other words, as shown in FIGS. 8A and 8B, a total of two tubes, a tube 114 for supplying ink 128 from a main tank 116 and a tube 115 connected to a suction generating device, such as a pump 117, are connected to one tank 111.
Although there are slight differences depending upon the frequency with which the inkjet recording head 101 is replaced, connecting means used in the structure shown in FIGS. 8A and 8B is generally and optimally constructed by providing openings 119 and 120 in the tank 111 of the inkjet recording head 101 and by closing the openings 119 and 120 by corresponding resilient joints 121 and 122, such as rubber plugs; and by mounting hollow needles 112 and 113 to ends of the corresponding tubes 114 and 115 and by passing the needles 112 and 113 through the corresponding resilient joints 121 and 122 and inserting them into the tank 111. The connecting means does not cause the ink 128 to drip even if there is a small amount of ink remaining inside the tank 111 when the inkjet recording head 101 is replaced. Therefore, in the connected state, the connecting means can reliably seal the tank 111 in order to construct an ink supply path with no ink leaks, thereby providing various advantages such as a simplified structure.
In the structure for supplying the ink 128 to the inkjet recording head 101, a carriage (not shown) which holds the inkjet recording head 101 is provided. The two hollow needles 112 and 113 are arranged vertically at a fixed position relative to the carriage. Holes 112a and 113a are formed in ends of or side surfaces near the ends of the corresponding needles 112 and 113. The upper needle 113 is connected to the pump 117 through the tube 115, and is constructed so that it can suck air in the tank 111 of the inkjet recording head 101 by operation of the pump 117. The lower needle 112 is connected to the main tank 116 through the tube 114, and is constructed so that it can supply the ink 128 in the main tank 116 into the tank 111 of the inkjet recording head 101. Therefore, by the pump 117, the air in the tank 111 of the inkjet recording head 101 is sucked through the tube 115 and the upper needle 113. In addition, the ink 128 is supplied into the tank 111 from the main tank 116 through the other tube 114 and the lower needle 112.
A mechanism for holding and securing the inkjet recording head 101 is provided at the carriage (not shown). By operating a carriage head lever, this mechanism can secure the inkjet recording head 101 to the carriage, and can allow removal of the inkjet recording head 101 from the carriage.
A mechanism for passing the two needles 112 and 113 through the resilient joints 121 and 122 of the inkjet recording head 101 and inserting them into the tank 111 is provided at the carriage. This mechanism may move in response to movement of the carriage head lever.
The least expensive method of detecting a timing of stopping an ink filling operation from the start of the ink filling operation is to stop the ink filling operation after a certain time from the start of the ink filling operation or after a certain amount of ink has been supplied. A more reliable method is to provide a special-purpose ink level sensor (not shown) inside the tank 111 and to stop the supplying of ink when the ink level reaches a certain height.
In the above-described related structure, the needles 112 and 113 are inserted into the tank 111 of the inkjet recording head 101 secured to the carriage. As shown in FIG. 8B, when the amount of ink inside the tank 111 of the inkjet recording head 101 becomes small, the amount of ink 128 around the needles 112 and 113 becomes small, so that the needles 112 and 113 are exposed to the air inside the tank 111. However, residual ink adheres to and remains on the outer peripheral portions of the needles 112 and 113 and the inside portions of the holes 112a and 113a, so that, when the needles are exposed to the air, the residual ink gradually hardens, causing the holes 112a and 113a of the corresponding needles to become clogged. When this occurs, the air inside the inkjet recording head 101 cannot be sucked and the ink 128 cannot be supplied through the needles 112 and 113. When recording operations are continued without any ink being supplied to the tank 111 of the inkjet recording head 101, not only does it become impossible to carry out recording operations when the tank has run out of ink, but also the inkjet recording head body 118 may break.
Accordingly, it is an object of the present invention to provide an inkjet recording head and an inkjet recording device which, as in the related structure, use a needle to supply ink to a tank of the inkjet recording head, but which addresses the problem of solidification of ink which might otherwise clog the needle.
Thus, according to a first aspect of the invention, an inkjet recording head includes a tank divided into a large capacity main chamber and one or more needle-receiving chambers. Each needle receiving chamber includes a connection hole for connection with the main chamber, and further includes an opening for insertably receiving a needle for supplying ink into (or discharging air from) the needle receiving chamber. In an upright position corresponding to a position of use of the inkjet recording head, the connecting hole is situated above the opening.
Because the connecting hole is situated above the opening, even in a situation where the ink level in the main chamber falls below the opening, a pool of residual ink tends to form in the needle-receiving chamber. This pool of residual ink completely encloses the needle and its terminal hole, such that the needle itself is not generally exposed to air and rather is enclosed by ink. Since the needle is not exposed to air, solidification of ink and clogging of the needle are largely reduced as compared with prior art devices.
In particularly preferred forms, the opening of the needle-receiving chamber is sealed by a resilient joint through which the needle can pass, so as to sealingly close the needle-receiving chamber during time periods when the needle is not inserted. In addition, the connecting hole has a diameter sized so as to facilitate formation of a meniscus of ink, thereby increasing the stability of the pool of residual ink in the needle-receiving chamber.
In further preferred forms, two or more needle-receiving chambers are provided, such as first and second needle-receiving chambers with corresponding first and second openings and first and second connecting holes. The first needle-receiving chamber is disposed vertically above the second needle-receiving chamber, when the inkjet recording head is in the upright position. Air is discharged from the upper first needle-receiving chamber, and ink is supplied into the lower, second needle-receiving chamber.
According to further aspects, the invention provides an inkjet recording device utilizing an inkjet recording head according to the above-mentioned description.
According to the above-described structures, an ink supply path, used to supply ink to the inkjet recording head, with minimal ink leakage, can be formed with a simple and low-cost structure. In addition, even if the amount of ink inside the tank has decreased, so that there is almost no ink inside the tank, the whole needle or at least a portion of the needle near the periphery thereof, since it is disposed in the needle-receiving chamber, is immersed in the ink, and not exposed to air so that solidification of the ink in the hole of the needle is largely avoided.
According to a second aspect of the present invention, there is provided an inkjet recording device comprising any one of the above-described inkjet recording heads, and supply means for supplying ink to the tank through the needle which is inserted into the needle-receiving chamber.
The inkjet recording device may further comprise discharge means for discharging air from the tank through a needle inserted into a needle-receiving chamber.
When the inkjet recording device further comprises discharging means for discharging air from the tank, the needle for the ink supplying means and the needle for the discharging means may be inserted into different needle-receiving chambers; or they may be essentially inserted at the same time in the same needle-receiving chamber.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.